The global positioning system (GPS) has been widely known as a satellite positioning system, and utilized for a car navigation system and the like. A GPS satellite signal is transmitted from each GPS satellite that orbits the earth. A GPS receiver calculates (locates) its current position based on the received GPS satellite signals.
A GPS satellite signal affected by a multipath or the like may be included in the GPS satellite signals acquired by the GPS receiver. The current position may not be calculated (located) accurately when using a GPS satellite signal affected by a multipath or the like. Therefore, the positioning accuracy may be improved by utilizing an altitude table (urban altitude information) in a multipath area in which a number of buildings such as high buildings are present (e.g., the center of Tokyo). The altitude table is a data table in which a central urban area having a small difference in altitude is divided into a given number of (i.e., nine) mesh areas and the altitude corresponding to each area is specified (see JP-A-2006-177783, for example).
A GPS receiver normally repeats positioning calculations for calculating the current position at given time intervals (e.g., intervals of one second), and outputs the calculated current position as the located position. The positioning calculations must be normally performed a plurality of times in order to output the first located position after starting positioning. A time to first fix (TTFF; time required to output the first located position after starting positioning) and the positioning accuracy have a relationship in which the positioning accuracy decreases when giving priority to a reduction in TTFF and the TTFF increases when giving priority to an increase in positioning accuracy. Whether to give priority to an increase in positioning accuracy or a reduction in TTFF is determined corresponding to the reception environment. For example, it is desirable to give priority to an increase in positioning accuracy over a reduction in TTFF in a reception environment with poor positioning accuracy (e.g., multipath environment) so that the located position is output after the Z-count included in the GPS satellite signal has been decoded so that the positioning accuracy has been improved. On the other hand, priority may be given to a reduction in TTFF in an open-sky environment with high positioning accuracy so that the located position is output without waiting for the Z-count to be decoded.